This specification relates to three dimensional (3D) printing using photopolymers.
Photopolymer-based 3D printers that use bottom-up illumination, project actinic radiation upwards through an optically transparent window into a vat of photoactive resin. As light passes through the resin, the photon flux is attenuated by absorption, and consequently the highest flux occurs at the resin-window interface. In the simplest model of photopolymerization, the polymerization rate is proportional to the square root of the photon flux, and accordingly the greatest polymerization rate also occurs at the resin-window interface. This phenomenon can result in adhesion between the window and formed polymer, in addition to adhesion between the printed part and the build tray, which lies further into the resin vat.
Photopolymer-based 3D printers that use bottom-up illumination typically address this issue by using a polydimethylsiloxane (PDMS) window, which is highly permeable to oxygen. During polymerization the oxygen dissolved in the window can inhibit polymerization at the window-resin interface, and can reduce adhesion between the polymer and window. However, the oxygen can be depleted from the PDMS, and polymerization can then subsequently occur at the interface. In addition, the polymerization is generally only inhibited immediately adjacent to the PDMS.